The present invention relates generally to metal shaping methods and more particularly to methods of producing moulded parts.
The invention may find application in the automobile, aviation and gas-chemical industries.
The method according to the present invention is suitable for producing parts both from metals and other materials such as plastics.
It is known that parts moulding methods are used most frequently when it is necessary to produce vessels capable of withstanding internal pressures of 10 to 500 and more atmospheres.
These vessels should meet special requirements with respect to their strength and operational reliability. Such vessels employed in the aviation industry should meet additional requirements, i.e. they should be of a minimum weight.
Blanks for the above vessels are usually produced by sheet metal stamping. The known method of producing moulded parts consists in that a flat sheet blank is moulded by 1-2-3 passes by means of a die and a punch having a shape similar to that of the part being stamped (spherical, tapered, flat-end).
In the conventional method of producing moulded parts a flat blank is placed on the die ring of a size of a part to be produced, then by means of the punch the blank is exposed to the action of pressure until a bend of a required radius is obtained in the moulding zone of the blank to give the latter the shape required.
Hard-to-deform materials such as titanium alloys are moulded at increased temperature of both the equipment and blank.
The principal disadvantage of the above method of producing moulded parts is that the walls of a part are thinned at the cupola portion of the part.
The degree of thinning reaches a value equal to 20-30% of the original thickness of the blank being moulded whereas during moulding of parts at increased temperature the degree of thinning of the walls of the part amounts to 50% of the original thickness of the material of the blank being moulded.
The thinning takes place due to the fact that at the commencement of the moulding process the punch exerts its pressure only on a small area of the blank and the maximum force should be applied to this area to start deformation of the entire blank.
The thickness of the blank at the point where the punch initially contacts the blank varies only slightly because of the force of friction between the surfaces of the elements mentioned, though the considerable thinning takes place in all nearby sections.
Due to this thinning of moulded parts, blanks are used of considerably larger thickness to give strength to vessels produced thereafter, which adds weight to the parts produced and causes excess consumption of materials.
In order to produce a moulded part of strictly limited weight, the part made from a blank of increased thickness undergoes machining, for example turning of external and internal surfaces of the product made. This machining is labor-consuming one and requires complex equipment. Moreover, machined parts are less durable and reliable than those made of sheet material. This is because of the disturbed structure of material as is the case with machining.
In addition, the known method of producing moulded parts is devoid of the ability to produce parts with an exactly given contour. Thus, round parts become elliptical both at edges and in cross sections. In order to correct the distorted shape, labor-consuming and expensive operations are used which in many cases do not provide the required accuracy are contour and therefore parts are stress-assembled (stress-welding of hemispheres) which impairs the reliability of joints.